The present invention relates generally to polyester compounds useful as plastic materials, especially polyethyleneterphthalate (hereinafter referred to as "PET") resins having good dimensional stability, excellent plasticity and a high degree of crystallization.
More particularly, the present invention encompasses PET resin compounds possessing good surface characteristics and physical properties as well as outstanding mold release properties when shaped even at a temperature of under 100.degree. C.
In conventional practice, PET is generally used for industrial purposes, for example, as a film fiber, due to its unique physical and electrical properties, its excellent thermal resistance and resistance to chemical degradation.
However, to be utilised in industrial fields requiring special type of crystallization, such as plastic processing, PET demonstrates peculiar crystallizing action during the process. Although PET is a crystalline polymer, several problems occur when it is used in plastic processes as a general thermoplastic resin with a metal mold temperature of under 100.degree. C. A high second order transition temperature causes the final molded product to have very low shape stability and to exhibit poor mold release properties. Long hours of operation are required to use PET resins in connection with metal molds. Undesirable stripe patterns or sink marks also typically appear on the product.
To solve the above described problems, Applicants have discovered that the temperature of initiating PET crystallization should be lowered and, at the same time, the speed of crystallization accelerated so that crystallization can be completed rapidly.
To speed up crystallization during processing at low temperature, certain inorganic substances are utilized. Talc, titanium dioxide, mica and magnesium oxide were introduced for such purposes in U.S. Pat. Nos. 3,368,975 and 3,575,931. Epoxy compounds were used as the accelerant for crystallization of organic substances in U.S. Pat. Nos. 4,276,208, 4,215,032 4,141,882 and Korean Pat. Publication Nos. 83-856 and 83-973. U.S. Pat. No. 4,366,273, British Pat. No. 2,075,301 and Korean Pat. Publication No. 81-1801, disclose the use of compounds including hydrocarbon metallic salts and unsaturated hydrocarbon polymer metallic salts containing carboxyl groups.
With respect to the inorganic substances described above, the effects, such as the formation of crystal nuclei, differ depending upon the distribution of particle-diameters and uniformity of dispersion. Desirable effects are not easily obtained even by increasing the quantity thereof.
The temperature under which crystallization is initiated is not easily lowered, and the crystallizing state of the surface of the final product processed at low temperature with a metal mold is normally in bad condition.
Where utilizing epoxy compounds as the expeditor of crystallization of organic substances, the physical properties of the organic compounds are not maintained. In the case of hydrocarbon polymer metallic salts, the plasticity deteriorates.